1. Field of the Invention
The present invention relates to a white die bonding material that is suitable for fixing a light emitting diode (LED) chip to a gold-plated substrate. More specifically, the invention relates to a heat-curable silicone adhesive for a semiconductor element that produces favorable chip positioning properties when a chip is pressed onto a substrate, exhibits high levels of concealment and adhesive strength, displays excellent durability, and effectively reflects light emitted from the chip.
2. Description of the Prior Art
Epoxy resins have conventionally been used as the die bonding material for fixing LED light emitting elements (chips). However, die bonding materials used for fixing blue or white LED light emitting elements (chips) tend to yellow over time upon extended use, and in a similar manner to that observed for epoxy encapsulating materials, the die bonding material tends to absorb light, causing a reduction in the brightness.
Nowadays, the demands relating to the durability of light emitting devices that use an LED as a module are even more stringent, and the LED encapsulating materials are gradually being replaced with silicone-based materials. In a similar manner to encapsulating materials, die bonding materials also require favorable durability, and it is expected that improved heat resistance will be demanded together with improved brightness. Die bonding materials formed from silicone resin compositions have already been proposed (Patent Document 1).
Silver electrodes and gold electrodes are typically used for LED electrodes, but in those cases where a silver electrode is used, oxygen permeation or the like through the encapsulating material can cause oxidation and blackening of the surface of the silver electrode, resulting in a deterioration in the light reflection efficiency. In contrast, in those cases where a gold electrode is used, because the electrode itself is inert, it offers the advantage of being unaffected by the surrounding environment. However, if a transparent silicone die bonding material such as that disclosed in Patent Document 1 is used with a gold electrode, then a problem arises in that the light emitted from the LED chip is absorbed at the gold surface, causing a deterioration in the light extraction efficiency. Accordingly, in order to improve the light extraction efficiency, for those cases where an LED chip is fixed to a gold-plated substrate, the development of a silicone die bonding material which blocks and effectively reflects light emitted from the LED chip, namely a silicone die bonding material with excellent concealment properties, has been keenly sought.
[Patent Document 1] US2006/0275617A1